fix: package.json & package-lock.json to reduce vulnerabilities (#786)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-JSYAML-174129

Author: snyk-bot

package-lock.json

@@ -93,7 +93,7 @@
     "js-yaml": "3.13.1",
     "less": "3.8.1",
     "lint-staged": "^8.1.5",
-    "mocha": "6.1.3",
+    "mocha": "6.1.4",
     "mocha-junit-reporter": "1.22.0",
     "mocha-parallel-tests": "2.0.3",
     "nock": "10.0.6",